Process of surfacing board and article therefor



n Jan. 3, 1933. w. A. DARRAH 1,892,873

PROCESS OF SURFACING BOARD AND ARTICLE THEREFOR Filed June 9, 1928 are 54.- v d [repen tar Patented Jpn. 3, 1933 PATENT OFFICE WILLIAM A. DARBAH, F CHICAGO, ILLINOIS PROCESS 0F SURFACING BOARD AND ARTICLE THEREFOR Application 'lled June 9, 1928. Serial No. 284,222.

` This invention relates to a process of surfacing board, the product of saidprocess and the equipment devised for carrylng out said process. y i

Some of the objects of this invention are to produce a strong, durable but light board at a low cost and with a minimum of equipment.

Cther objects of this invention' are t o prolo duce a board having a greater flexibillty than' is customary with present boards.

This invention also discloses a means of producing a board which is a more suitable base for holding plaster or other finishes. Thls invention gives a board which 1s water ressting or Water-proof. Other obJects of this l invention will be apparent in the dlsclosure which follows in this specification.

In the specification and claims the term board is used to denote a material havlng a relatively large ratio of surface to volume.

applicable to such materials as are now known y 5 as wallboards, straw boards, fibre board, cardboard, chip board and related products. The exact thickness of the board to which this invention may be applied isnot of prime im-y portance. For purposes of illustration, the invention will be discued as applied to cellulose containingwallboards which normally average between three-eighths and onehalf inches in thickness and are made from felted cellulose fibres. are made from Wood pulp, bagasse, straw, licorice root, peat, corn stalks and various other cellulose materials. I do not wish to confine this invention to any particular kind or type of board as obviouslyit can be applied to advantage to the boards mentioned,

cellulose with other materials since someof the processes and reactions disclosed depend upon presence of cellulose material. Some of the phases of this invention, however, are

Boards of this class' broad enough to cover other applications as will be evident from the disclosure.

It is now customary to produce boards in the class described with a substantially uniform texture throughout. In other words, boards of this class are ordinarily produced with an interior composition substantially identical with the exterior condition. In the case of the felted fibres, a simple felt is produced by well known methods from a mixture of he desired fibre with certain sizing mater1a s.

In present boards, it is customary to pro- -duce a relatively soft board for a number of reasons.

The softness of the board means with present methods Aa light board for a given thickness. Since the board is light it contains relatively small amounts of material and, therefore, involves a lower cost than a denser or harder board. The lightness of the board also serves to, reduce freight and handling expenses and of course ives a measure of insulation which adds to t 1e usefulness of a board.

At the same time the lightness of the board involves a weakness since the board is relatively soft and easily broken or torn. The porous structure also renders the board somewhat absorbent of Water and as a result, the board cannot be considered water-proof. This virtually requires'a limitation of application of present boards to instances where they will not be exposed to normal Weather condition.

My invention involves the means at relatively small expense of applying a surface coating to the boards also composed largely of cellulose material, the coating making the 'board much harder at the surface than on its interior.-

The coating may be applied to one or both surfaces or of course, if desired to the edges although ordinarily this is not required.

It t,will be apparent that a board having a strong tough surface is much more durable than a board having a soft surface of the same material as the interior. The addition of the hard surface gives the board strength against bending or deforming at exactly the point Where the strength is required. For

example a board which might be made hard in the interior and soft on'the surface would have much less strength than a board hard on the surface, since in bending or deforming the board the fibres on the surface are subjected to the greatest strain.

It will also be apparent that if the sur-` face of the board can be protected from the entrance of water that the board will have a much wider field of application. It will be apparent that the additional material and additional weight required to increase the strength of the surface of the board will be very much less than the materials required to produce a similar degree of strength throughout the entire cross section 0f the board. Further by forming a surface which interlocks with the fibres which make up the interior of the boards, the strength of the composite material is greatly increased.

Referring to the drawing: i

. Fig. l indicates a cross section of a present type of commercial board produced from fibres in the usual commercial manner;

Fig. 2 indicates a cross section of the board made in accordance with one form of my invention;

Fig. 3 shows on an enlarged scale a cross section of one form of my board and indicates a surface layer interlocked with the interior bres;

Fig. 4 shows in elevation and diagrammatically a board making machine operating in accordance withmy invention;

Fig. 5 shows in vertical elevation also diagrammatically one form of carrying out my process and the equipment employed;

Fig. 6 is a vertical end elevation in section of the equipment shown in Fig. 5.

Referring to -the drawing, 1 indicates a present form of commercial board while 2 indicates a board made in accordance with my invention. 3 and 4 indicate the surface coating which is shown interlocked with fibres 5 and 6. 7 indicates a standard commercial type offelting machine and shows a stock box 8 containin the fibres in suspension in water, the ma ing rolls 9 and the finished felt 10 leaving the making machine. 11 indicates a dryer which may be of any commercialtype and is shown diagrammatically as any device for removing water from the felted board. The dried board leaving dryer 1'1 is shown at 12 passing .throughthe inspection section 13 into surfacing machine 14. .The board leaves surfacing machine 14 on a series of conveyor rolls 15, and travels through dryers and cutting machines or other standard equipment not shown.

Cutting machine 14 is provided with a series of rollers 16 vwhich serve to convey the board through the treating device. The device is preferably enclosed and insulated by walls 17, 18 and 19 which rinsure maintaining the desired temperature and desired atmosphere within the cutting device. A series of heating members 20, 21, 22 and 23 areused to assist in drying and maintaining the desired' temperature within device 14. On entering device 14 thc board passes through a` pair of rolls 24 and 25 which serve to supply a slurry of definite composition as later described. Upper roll 24 is supplied with slurry from intermediate roll 26 which connects with supply roll 27 which rotates in container 28, containing thc desired liquid. Container 28 is supplied with heat from steam coils 29 or other source as may be desired. Lower roll 25 rotates directly in tank 3() which is supplied with heat from member 3l. The heating members may to advantage be controlled thermostatically in order to insure a uniform temperature at all times. Container 3() is provided with a drip extension 42 to drain back into the con tainer any of the treating liquid which may drip off. It will of course be understood that the rolls, containers and associated parts eX- posed to corrosive materials will be formed of proper non-corrosive ingredients such as lead, monel, glass, etc.

After passing between treating rolls 24 and 25, the board travels forward in the direction shown by the arrow and passes between working rolls 32 and 33. These rolls are re- Volved 1n such a. manner as to cause a rather rapid relative travel between the board and the surface of the roll. either in the same direction as the travel of the board, but at a higher velocity or they may travel in the opposite direction as desired. The object of the rolls 32 and 33 is to work the surface of the board and lalso in some cases to leave the board with a smooth polish. In applying many solvents an advantage is found in rubbing or working the surface fibres while in contact with the slurry as this appears to assist in the reaction upon the cellulose.

24 indicates one of a series of rollers which serve to convey the board through the treating process. A series of treating units are shown in Figure 5 and inasmuch as the va'- rious units are substantially identical in principle no description of the other units will begiven. 35 indicates a hopper containing powdered material while 36 is a duct or channel by which such material may leave hopper 35. 37 indicates a flow control device such as a feeder and is used to control the rate at which thematerial 38 in hopper 35 is applied to the surface of the board.l 39 indicates an air line, 40 anair valve and 41 a nozzle for applying powder 38 to the surface of the board. This equipment may be dupli` They may travel cated for applying powder to the underside of may penetrate the board. For example if I wish to gelatinize the surface fibres of a felted board, I have found that if applied in the form of a liquid the gelatinizing material will rapidly penetrate the entire board. For example if I use sulphuric acid wit-h a concentration of two parts o'f acid to one part of water, I may obtain a very effective solution of the cellulose material, but if' applied in a liquid form the react-ion proceeds irregularly and results in forming deep holes or pits in some parts of the board, while attaching other parts only slightly. Further the reaction is only controllable as to time and a very slight variation in the duration of contact between the acid and the board will cause wide variations in the result. A free solution under certain conditions may char the fibres.

The above conditions would naturally be expected in treating a material which in a way resembles blotting paper and is highly absorbent of most liquids.

In order to overcome this result and produce a controllable coating, I have found it expedient to mix with the treating liquid a carrier which may be of fine powder. a viscous liquid or a gelatinous material. For example in the case of sulphuric acid. I have found that commercial gypsum (plaster of Paris) forms a very eli'ectife material when added in such amounts that the resultant mixture is about as thick as cream. Under these conditions. the attraction between the slurry and the acid balances the attraction between the acid and the board, thus controlling the depth of which the reaction may proceedA and retarding the reaction sufficiently to make it readily controllable while, at the same time utilizing concentrated materials. will be evident that the addition of water to the acid would dilute the acid and retard the rate of reaction but not the depth of penetration. The equivalent addition of' water, I have found, in no Way serves the purpose of the addition of the viscous materials as described.

It may be noted that burned gypsum (plaster of Paris) does not readily set when used 1n this mlxture probably because the necessary transfer of water is yprevented and the growth of crystals eliminated. In place of gypsum I may add clay of various kinds. fullers-earth. finely powdered silica or any one of alarge number of materials which are relatively inert in the presence of the gelatinizing material and serve to form a plastic viscous slurry. I Inay also add thick liquids such as glycerin although these are not ordinarily so available as the solids. In the case of other solvents thalrsulphuric acid. I have found a solution of zinc chloride preferably containing free hydrochloric acid preferably mixed with ful`ers-earth very effectively,particularly if slightly warm. I have also found that :solution of copper oxide in ammonia produced in the well known way and mixed with aluminum hydroxide makes a very effective slurry. I may also use caustic alkalies such as sodium hydroxide carrying in solution aluminum hydroxide or other gelatinous or slurry forming materials. I have also found that a solutionof fine ground lime in caustic soda makes a very effective alkaline slurry as well as aslurry of ground caustic burned magnesite containing sodium hydroxide in solution, as the liquid material.

From the above discussion, it will be apparent that the desirable elements in the slurr which I use consist of a medium for attac ring the cellulose, carrying a thickening or retarding medium. Various modifications or additions may be made as for example in the case of sulphuric acid I may add an amount of nitric acid which materially hastens the reactions, but introduces some difficulties otherwise, by reason of the fumes produced. l

In carrying out my process, I find it to advantage to first apply my slurry as described above uniformly over the entire surface of the board or sheet. I may apply this to one or both sides of the sheet depending on the required application. The slurry is then allowed to stand in contact with the sheet for a definite period while the sheet travels forward through the process machine. The next desirable step is to agitate or rub the surface of the board which results in rubbing the slurry into the pores and produces a somewhat more uniform and deeper reaction. During this time the board is maintained in a warm atmosphere at a controlled temperature with the desired humidity preferably to prevent the material loss or gain of moisture from the slurry. It will be apparent that if desired I may omit the rubbing or working action and still come within the spirit of my invent-ion as the effectiveness of this step depends upon the texture and composition of the board as well as the nature of the slurry and the desired surface.

I may next remove the excess slurry by treating rolls similar to 24 and 25, but supplied with a washing solution instead ofcarrying a slurry. The washingsolution may either be water or a solution of a salt in water as for example in the case of the treatment of the board with sulphuric acid, the washing solution may be a soluble. sulphate dissolved iu water as for example sodium sulphate.v rThe advantage of a concentrated solution of this kind lies in the fac-t that it removes the excess of slurry and does not necessarily dissolve large amounts of acid. I may of course if desired use other solvents or only pure water. The next step consists in applying the neutralizing material. This may be an alkaline slurry in case the first slurry applied is acid in character or if the first slurry applied is alkaline this slurry would be acid in,

character. In some cases I prefer to apply the neutralizingslurry without a previous washing, as I thereby obtain a more active combination between the gelatinous cellulose compound and the neutralizing slurry.

In case I wish to prepare a surface which contains the minimum amount of mineral ingredients and the maximum amount of cellulose, I prefer to remove the first slurry, wash the surface and apply the second slurry followingit by a second washing. In some cases, I find it highly expedient to prepare a surface containing large amounts of mineral ingredients as for example in' soluble sulphates, chlorides, oxychlorides, oxides in which case I may omit the washing action.

For example if I first treat the board with a slurry which consists' of zinc chloride, hydrochloride acid and fullers-earth then work the surface of the board and finally apply a slurry of caustic burned magnesite mixed with sodium hydroxide in water, I obtain a resultant surface which contains cellulose, partially treated fibres and magnesium oxychloride. This gives a strong', hard and closely adhering surface, the 4thickness of which is readily controllable by varying4 the time of treatment, concentration of theingredients used and other factors.

It will be noted, therefore, that this invention contemplates a hard surface formed upon a board, the surfacev containing appreciable amounts of cellulose. I have outlined various methods of obtaining such a surface .in order to showthe scope of my invention and various other compositions and types of surfaces may readily be made by those skilled in the art without departing from the scope of my invention.

It should be understood that my invention is not confined to any special thickness or type of board, although I prefer to apply itA primarily to boards containing relatively large percentages of cellulose in other composition. The presence of other materials ina board does not of course reclude the carrying out of my invention. Imay face either one side or both sides of the board, but do not wish to be confined to any special arrangement in this matter. In using the term acid and alkali I am employing them broadly and by referring to cellulose dissolving material I intend to indicate those materials which attack and combine with cellulose although many of them do not form a true solution in the strict sense. These features are Awell known to those skilled in the cellulose industries.

The factor of working or rubbing the surface of the board appears to be very helpful in obtaining Aa smooth uniform coating, but is not essential in carrying out the process of my invention.

It will be apparent that in addition to de-l vising a new process for treating boards and an apparatus for carrying out this process, I have also invented a new board which has novel and vdesirable characteristics compared i to boards'now available'on the market, and I consider'the product part of my invention. It will be apparent that if desiredImay neutralize the coating first applied by a spray of liquid v0r of dust or powder although I prefer the roller method already described. However, it will be apparent that the resultant board which I have invented may be obtained by such a method. In the case a liquid with the chemistry envolved. On the other hand, I may in some cases omit entirely any neutralizing of thefsurface layer allowing the material added to the surface of the board to in effect neutralize themselves by reacting with t'he board. For example when a slurry of sulphuric acid carrying calcium sulphate in suspension in added to the surface ofthe board and removed, the surface becomes hard and dense?withoutneutralization. i

One method of treating the surface of the board, which I have found very satisfactory, consists in first addinga solution of sodium silicate preferably containing an'excess of caustic soda, but not necessarily s0. Such a solution when hot directly attacks the cellulose forming a jelly or semisolution. By then adding to the surface of the board after the application of the silicate solution. (and permitting proper time interval for thereaction to take place) a concentrated sulphuric acid slurry or solution, I am able to precipitate in the surface layer of the board a mixture of silica, calcium silicate. gelatinized cellulose 'and cellulose fibres. This mixture adheres strongly to the fibresand the balance ofthe board and when. polished by a rapidly revolving roll rubbing on the-surface of the board gives a smooth, hard finish of the type which I had invented. If the polishing 4roll is hot the surface usually hardvens more rapidly and givesl a more uniform o surface. i A

If desired I may add color or stain such as oxides or dyes,thus producing a board having a colored surface.' For example by adding ferrie compounds to Athe sulphuric acid slurry, I am able-to produce a board having 4a rich reddish brown color which somewhat resembles mahogany. Various other colors may be produced at will by the addition of proper ingredients.

It will be apparent that more rapid reaction will take place in the case of the various materials applied in case the board is kept warm and further the final drying will proceed more rapidly and vmore uniformly in case the board is Warm during treatment.

It should be understood that-the order in which the various reagents are added to the surface of the board is in some cases of great importance.

For example in the case of the'coating formed by precipitating a soluble silicate among the surface fibres this result is readily obtained if the silicate solution is added to the board while if the acid solution is first added to the board the silica precipitate forms above the board and will not adhere to the surfacenor form a coating with the fibres. In general .it may be stated that the material rst added to the fibres will be the one which Will supply the major portion of the ingredients in the precipitated film.

A It will be understood that where mention is made of acids or alkaline, I do not wish to be restricted to free acids or alkaline as used in the ordinary sense', but rather intend to convey the idea of mediums whichvhave an acid reaction. For example alum, ferrie chloride or various other easily hydroxized salts will in many cases produce the same effect as a free acid. In the same way many salts may produce the effect of a free alkali Y as for example sodium silicate or combinations of a strongly basic element with a Weakly acid radical. Y

Having now fully described my invention what I claim as new and wish to secure by Letv ters Patent in the United States is as follows:

Vl. An article of manufacture consisting of a board of material thickness composed mainly of cellulose material having an absorbent core and with a hard surface containing chemically altered cellulose.

2. An article of manufacture consisting of a board of material thickness composed mainly of cellulose material with a soft core and a hard surface composed of altered cellulos mixed with mineral material.

3. An article of manufacture consisting of a board of material thickness having an interior of relatively soft and porous structure and a surface of relatively hard and dense structure, containing chemically altered cellulose and mineral material.

4. An article of manufacture consisting of a board of material thickness composed mainly of cellulose material having an interior portion with a relatively porous and absorbent structure and a chemically altered surface which is relatively dense, smooth and water resisting.

5. A board of substantial thickness formed mainly of interlocked cellulose fibres in the' interior with a surface consisting largely of cellulose libres intermingled with an insoluble compound of silica.

6. A board formed `mainly of cellulose fibres having a relatively soft interior and a relatively hard smooth surface containing a mixture of chemically alteredcellulose and mineral matter precipitated together.

7 rIhe process of treatin the surface of cellulose board to a control ed de th which consists in first ap lying to the sur ace of the moist board a limited quantity of the slurry7 containing a cellulose dissolving 'materia second working said surface, third removing the excess of said slurry and finally drying said board in a substantiall fiat condition.

8. The rocess of manu acturing cellulose board which consists in forming said board from a liquid suspension of fibers, pressing and partially drying said board and finally applying a slurry 'containin cellulose dissolving material, allowing sa1d slurry to act for the desired period upon the moist surface of said board and then dryinglsaidboard while substantially Hat.

9. The process of forming a cellulose board which consists in felting the fibers composing said board, pressing said felting fibers and removing some of the moisture containedy in said web then applying to the surface of said moist board a slurry containing cellulose dissolving material and after allowing said slurry to act upon the board to a controlled depth, neutralizing said slurry and drying said board in a substantially flat position.

10. The process of forming a board having a hard surface and a porous interior which consists in felting` the fibers for said board into a web, pressing and partially drying said web, applying a slurry containing cellulose dissolving material to the moist surface of said web until the surface is transformed while the interior is substantially unaffected, and finally neutralizin the excess of said slurry and drying said oardwhile substantiallym fiat.

11. The process of forming board which consists in felting the fibers from a water suspension, pressing the resultant web, rolling into the surface of said resultant web While still moist a treating slurry, and finally drying said resultant product on a series of moving rolls at an elevated temperature.

' WILLIAM A. DARRAH. 

